## FitGamma

##### >Psychtoolbox>PsychGamma

[fit_out,x,fitComment] = …

FitGamma(values_in,measurements,values_out,[fitType])

Fit a gamma function. This essentially a driver function.

It has two main purposes.

First it tries several different

underlying parametric forms for the fit and chooses the best

for a particular data set.

Second, it does the bookkeeping for fitting each column of

input measurements. (Each of the underlying fit functions expects

only vector input.)

To a large extent, the interface to the underlying fit functions

(e.g. FitGammaPow, FitGammaSig, …) is uniform. However, this routine

does have to know a little bit about initial value dimension and choice.

We have tried to localize this information in the initialization routines

(e.g. InitialXPow, InitialXSig, …) as much as possible, but some

caution is advised.

Optional argument fitType allows you to force the return of a particular

paramtetric form. Currently:

fitType == 1: Power function

fitType == 2: Extended power function

fitType == 3: Sigmoid

fitType == 4: Weibull

fitType == 5: Modified polynomial

fitType == 6: Linear interpolation

fitType == 7: Cubic spline

All fit types are in a form such that the fit is forced through the

origin for 0 input. This is because our convention is that gamma

correction happens after subtraction of the ambient light.

NOTE: FitGammaPow (and perhaps other subroutines) uses CONSTR, which is part of the

Mathworks Optimization Toolbox.

Also see FitGammaDemo.

`Psychtoolbox/PsychGamma/FitGamma.m`